It doesn't load quickly unless you avoid Plex servers, because authentication happens through them.
Jellyfins interface is great what are you talking about? Easy, quick and to the point. Does exactly what I want.
Plex cant make up its mind what to do as they keep making it worse. More clicks to get anywhere and adding their own crap all the time.
Sorry, Plex is a mess. I just opened it now, and its so bad.